1. Field of the Invention
The invention relates to printing apparatuses and printing systems that are capable of performing calibration and preparing new color profiles for print mediums that were not intended for printing in advance.
2. Description of the Related Art
In recent times printing apparatuses and printing systems have been offered that perform calibration for print mediums that were not intended for printing in advance and generate new color profiles therefor, in order to output images having stable density and coloring on a variety of types of print mediums. Such a printing apparatus or printing system prints a prescribed pattern on such print medium, measures the color of the pattern using a color measurement device, and performs calibration and generates a color profile based on the color measurement result.
The calibration in the specification herein is a function for stabilizing the image density expressed on a print medium regardless of the type of print medium. In order to achieve this, for example, input signal values are converted to a lower level in the case of a print medium for which the density has a propensity to be expressed high, and input signal values are converted to a higher level in the case of a print medium for which the density has a propensity to be expressed low. In order to perform such conversion processing a 1D conversion table, in which suitable correction output signals (C′M′Y′K′) are associated with the respective input signals corresponding to each ink color (CMYK), is prepared for each print medium.
On the other hand, the color profile generation function in the specification herein is a process that applies a correction to the input signal values such that for every type of print medium the same chromaticity is expressed with respect to the same input signal combination (RGB). In order to perform such conversion processing a multivalue conversion table, in which suitable output signals (R′G′B′) are associated with each of the input signals (RGB), is prepared for each print medium.
In order to create conversion tables with respect to both calibration and color profiles an operation is required in which a prescribed patch is printed on the target print medium, the color of the patch is measured, and the conversion table is generated according to the result of the color measurement.
Here, in the case where a printing system performs printing only on selected types of print mediums, conversion tables may be made in advance that correspond to the various print mediums and stored in advance within the internal memory of the printing system. In recent times where various print mediums are offered, however, there are times where printing is also performed on print mediums that were not intended for printing in advance, and there is a risk it will not be possible to express the target density and the target chromaticity. If the printing system is provided with a color measuring device, however, even in the case where a new type of print medium is mounted it is possible to perform an operation wherein the above operation, that is, an operation in which a prescribed patch is printed on the print medium, the patch is measured, and a conversion table is generated according to the color measurement result. By way of using a newly generated conversion table, it becomes possible to express the target density and the target chromaticity on the print medium.
It is not the case, however, that the above described operation for generating a conversion table can be correctly performed for all print mediums. For example, color measurement results are often not stable for print mediums in which there is severe surface roughness and optical conditions cannot be held uniform, and for print mediums in which the lightness, chromaticity, and glossiness are not uniform on the surface. Thus a problem occurs wherein when a conversion table is generated based on such an unstable color measurement result it is not possible to perform a correction with a high degree of reliability and only an undesired color reproduction can be obtained.
Furthermore, in the case where the base color of a print medium has a high color saturation of hue such as yellow, although it is possible to perform a set of operations and to generate a conversion table, influence of the base color will be included in the color measurement result. Thus even if the generated conversion table is used it is difficult to suitably correct shifts of hue and saturation that are expressed on the print medium by applying ink, and there are cases where a mistaken reproduction of color occurs in the output image.
In order to prevent such an undesired color reproduction Japanese Patent Laid-Open No. H05-024224 (1993), for example, proposes a method of excluding print mediums that are not adaptable to the apparatus by way of the printer maker marking multiple types of print mediums in advance and reading the marks with a sensor. In the method of Japanese Patent Laid-Open No. H05-024224 (1993), however, there is a limit to the types of print mediums on which it is possible to apply a mark, and it is not possible to sufficiently handle unknown print mediums that a user has prepared on his or her own.
That is, before the invention disclosed herein, in an environment where various print mediums existed in the marketplace, it was not possible to reliably determine with respect to all print mediums whether or not it was possible to generate a correct conversion table for calibration and color profile correction.